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Dead 850?


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My 850 doesn't seem to be working anymore. I'm assuming the ultimate test is to try to boot with the 850 being the only device on the SIO chain, but this doesn't give me a response either.


Any ideas on where to start troubleshooting?




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Edited by gozar
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When you boot only the Atari and the 850 do you hear about 1 second of beep tone(s)? Get the typical long *fart*? or something else?


Are you using the right power supply?



I don't have an 850 to test but if you connect the 850 and an SIO2PC you might be able to see the SIO activity in the disk emulator's monitor. You'd have to turn off printer emulation in the disk emulator. SIO2BSD's printer emulation is off by default. I don't remember whether you can, can't or need to in the other disk emulators.

Edited by a8isa1
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No affect with different power supplies and SIO cables. :-(


It sits on the long farting noise like nothing is attached before going to self-test. I know what the normal SIO sound should be with its long beep.


Same response on two different machines. I guess next I need to open it up!

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um with just the 850 attached... nothing else.... no internal sio2sd etc.... you don't get basic?


reseat the 850's chips... leave it on for a day, make sure the sio cord is good try again...


Maybe he's using a 1200XL?

​Personally I'd open it up and look for a leaky cap or a cold solder joint somewhere on the board, especially around the power jack. Then I'd reseat all the chip - I'd actually remove them all, look for damaged or corroded sockets, then reinstall them. If still no luck, it might be time to start sourcing replacement parts and doing the old substitute chips trick and you get it working again. Might be cheaper/easier just to find a new-to-you working 850.

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If, after you open it up and don't see any obvious problems, and after you remove and reseat all the IC's, and if you have a volt meter; look for the voltages in the attached

picture (out of the 850 field service manual) for the correct voltages. If the correct voltages are there and it still won't boot up after you've removed and reseated all the

chips, you've most likely got a bad chip(s)




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okay, lets take this from another perspective..


no boot is 'Usually' a problem with 5v or 10v supply either out of specification too low or too high... I don't usually follow the 850 FSM in procedure the difference is I pull the loading chips first so I can see the voltages and ripple right off the bat, then I add the loading chips back to determine the failed chips...or if the supply is failing under load, it's always been faster that way...


hoping to start simple but maybe it's best just to provide the FSM and have at it :)



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